It seems to me that Mix Copy is not where you would expect to find it.
IMO the most intuitive is in the LR or Bus channel overview. (Seeing as you are copying the LR or Buss mix)
Could be nice to have a long press on the SoF button to open this too - but of course that could be created in a button in Layout edit.
It may be handy to leave it also available as it is currently.
Hope the above is helpful - will leave it there for now as I don't want to overwhelm you with requests and bug reports!
Many thanks again for great software and being so responsive to users.